1. Field of the Invention
This invention relates to a treated basic converter slag and a process for treating the basic converter slag, and more particularly to the slag and a process of the type described in which iron or manganese components are converted into forms which allow easy recovery thereof.
2. Description of The Prior Art
In general, basic converter slag contains about 10 to 20% (by weight) iron in terms of a total iron content, and the amount of slag produced is considerably large. Hithereto, many attempts have been proposed for the recovery of iron from slag by crushing and mineral processing techniques for the reuse of slag as an iron resource. However, the recovery yields attained are extremely low, and the result is that only a portion of the slag is recovered, while a majority of the slag is used only for reclamation purposes.
A difficulty encountered by the mineral processing recovery technique lies in that a majority of the iron component contained in basic converter slag is present as divalent wustite, and that the phosphorus components which are detrimental components for the reuse of slag are apt to remain in the slag, without being removed therefrom.
As indicated in Table 1, the composition of untreated slag after the completion of the converter steel making process substantially consists of five phases, i.e., a di-calcium silicate, tri-calcium silicate, wustite, lime, and di-calcium ferrite including titanate which is in the form of a solid solution therein (Di-calcium ferrite and titanate perovskite solid solution, hereinafter.). In addition to these components, luppe, CaF.sub.2 (fluorite) and calcium aluminate are present in the slag in small amounts. (Meanwhile, the aforesaid tri-calcium silicate and lime are present only in slag of a high basicity.) As can be seen from Table 1, a majority of iron components other than iron droplets are present in both phases of wustite and di-calcium ferrite perovskite solid solution, and iron components other than iron droplets are all non-ferromagnetic, thus not allowing screening and recovery by a magnetic separation process. On the other hand, the phosphorus components which are detrimental in this case are present principally in the di-calcium silicate phase. (In this respect, if CaF.sub.2 is added in a great amount, the phosphorus components are present in the form of calcium fluoro-phosphate.) In this manner, the iron components present in untreated slag are dispersed in the aforesaid phases, respectively, while the oxidized states thereof vary, so that a chemical separation technique is quite difficult to apply. In addition, a magnetic separation process is not useful for the separation of iron components other than iron droplets, because of their non-ferromagnetic properties.